This invention relates to an improved process for the purification of a hydrogen stream by low temperature multistage partial condensation of impurities. The contaminants include methane, ethane, and in some cases heavier hydrocarbons as well as inert gases, and the process of the invention is conducted under pressures of above 100 bar.
In the conventional condensation process, the gas to be purified is cooled to condense out the heavier components which are then removed stepwise in separators. At the end of the cooling step the gaseous stream contains only light components of a specific purity depending on the initial gas composition and the final temperature.
The number and arrangement of the selected separators depends on the type of raw gas being purified as well as by two criteria. On the one hand, it is essential to separate heavy components before they reach the freezing point so as to prevent fouling of the flow passages, and, on the other hand, from an energy viewpoint, there is to be avoided the cooling of relatively large amounts of condensed out liquid to lower temperatures and the reheating of same after their separation.
Therefore, it is conventional in the purification of a hydrogen stream containing light hydrocarbons to arrange the separators in such a way that almost all of the C.sub.2 -hydrocarbons can be separated with the next-to-last condensate. For this purpose, using a C.sub.2 -refrigerant, a temperature is required of about -100.degree. C. In the subsequent final condensation stage, a condensate is then obtained which is essentially methane.